Organometallics 1996, 15, 3637-3639
3637
A Chiral Triamidostannate: Its Structure and Properties as a Nucleophile† Harald Memmler, Uta Kauper, Lutz H. Gade,* and Dietmar Stalke Institut fu¨ r Anorganische Chemie der Universita¨ t Wu¨ rzburg, Am Hubland, D-97074 Wu¨ rzburg, Germany
Joseph W. Lauher Department of Chemistry, State University of New York, Stony Brook, New York 11794 Received May 1, 1996X Summary: The first enantiomerically pure chiral triamidostannate, HC{SiMe2N[(S)-CH(Me)Ph]}3SnLi(THF) (2), has been synthesized and structurally characterized; the crystal structure of the derived Sn-Ni heterobimetallic complex [Li(THF)4][HC{SiMe2N[(S)-CH(Me)Ph]}3Sn-Ni(CO)3] (5) is reported. The versatility of organotin compounds in organic synthesis has recently fueled the development of chiral stannanes with the aim of effecting enantioselective transformations using these reagents.1 Whereas all the reported species of this type are derivatives of tetravalent tin,2 there has so far been no example of an enantiomerically pure chiral tin(II) compound in the literature. The anionic stannates(II), in particular, are valuable metal nucleophiles3,4 which may be transformed to the corresponding stannanes by simple nucleophilic substitution or addition reactions.5 The facile accessibility of triamidostannates containing a tripodal amido ligand6 along with the possibility of generating enantiomerically pure C3-chiral tripod ligands provided the motivation for the the synthesis of a chiral stannate and a study of its properties as a metal nucleophile. Lithiation of the previously reported triamine HC{SiMe2NH[(S)-CH(Me)Ph]}37 with 3 molar equiv of n-BuLi and subsequent reaction with SnCl2 gave the chiral stannate 1 in almost quantitative yield as evidenced by NMR spectroscopy (Scheme 1). Using THF as the reaction medium for the lithiation or addition of THF to 1 led to the isolation of the monosolvated species 2. The 1H, 13C, and 29Si NMR resonances of the stannate unit in both 1 and 2 indicate the reduction of its potentially 3-fold symmetry due to † We dedicate this paper to Professor Max Herberhold on the occasion of his 60th birthday. X Abstract published in Advance ACS Abstracts, August 1, 1996. (1) (a) Marshall, J. A. Chem. Rev. 1996, 96, 31. Yamamoto, Y., Ed. Organotin Compounds in Organic Synthesis. Tetrahedron 1987, 45, 909. (b) Omae, I. Organotin Chemistry; Elsevier: Amsterdam, 1989. (2) Nozaki, H. In Organometallics in Synthesis-A Manual; Schlosser, M., Ed.; Wiley: New York, 1994; p 535. (3) Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in Organic Synthesis; Butterworths: London, 1987. (4) Studies of solid-state structures: (a) Reed, D.; Stalke, D.; Wright, D. S. Angew. Chem., Int. Ed. Engl. 1991, 30, 1459. (b) Veith, M.; Ruloff, C.; Huch, V.; To¨llner, F. Angew. Chem., Int. Ed. Engl. 1988, 27, 1381. (c) Hitchcock, P. B.; Lappert, M. F.; Lawless, G. A.; Royo, B. J. Chem. Soc., Chem. Commun. 1993, 554. (d) Steiner, A.; Stalke, D. J. Chem. Soc., Chem. Commun. 1993, 1702. (e) Steiner, A.; Stalke, D. Inorg. Chem. 1995, 34, 4846. (5) Fieser, M. Reagents for Organic Synthesis; Wiley-Interscience: New York, 1990; Vol. 15. (6) (a) Hellmann, K. W.; Steinert, P.; Gade, L. H. Inorg. Chem. 1994, 33, 3859. (b) Hellmann, K. W.; Gade, L. H.; Gevert, O.; Steinert, P.; Lauher, J. W. Inorg. Chem. 1995, 34, 4069. (7) Memmler, H.; Gade, L. H.; Lauher, J. W. Inorg. Chem. 1994, 33, 3064.
S0276-7333(96)00324-X CCC: $12.00
Scheme 1
direct coordination of the cation to the tripodal triamidostannte anion.8 The mode of coordination of the Li+ or Li(THF)+ cation was established by a single-crystal X-ray structure analysis of 2 (Figure 1).9 This revealed its position as bridging between two amido N atoms, a situation which leads to a remarkable distortion of the stannate cage. The Li atom “ties” the two amido functions involved together, generating an N-donor arrangement which deviates from the otherwise more or less undistorted trigonal-monopyramidal arrangement of the N3Sn unit (N(1)-Sn-N(3) ) 82.6(2)° but N(1)-Sn-N(2) ) 99.2(2)° and N(2)-Sn-N(3) ) 102.0°). Another structural consequence of the direct bonding of the amidostannate to the cation is the rotation of the SiMe2 groups at Si(1) and Si(3) to an almost eclipsed arrangement, which (8) Preparation of 1 and 2: To a solution of HC{SiMe2NH[(S)-CH(Me)Ph]}37 (1.35 g, 2.49 mmol) in 30 mL of diethyl ether which was cooled to -50 °C was added 3 mL of a 2.5 M solution of n-BuLi in hexanes, and the reaction mixture was warmed to ambient temperature within a period of 1 h. After recooling to -50 °C solid SnCl2 (0.50 g, 2.63 mmol) was added; the reaction mixture was then warmed to room temperature and stirred for another 1 h. Removal of the solvent in vacuo and extraction with pentane yielded a solution of the crude product which was concentrated to 15 mL and left to crystallize at -20 °C. 1 was obtained as a colorless solid in 47% yield. Crystallization from a mixture of pentane-THF (1:1) afforded the solvated species 2 (yield 39%). Data for 1 are as follows. 1H NMR (C6D6, 295 K): δ -0.92 (s, HC(Si...)3), -0.71, 0.08, 0.30, 0.37, 0.40, 0.43 (s, Si(CH3)2), 1.36, 1.49, 1.90 (d, 3JHH ) 6.9, 6.7, 6.7 Hz, HCCH3), 4.32, 4.42, 4.96 (q, HCCH3), 6.75-7.74 (m, C6H5). 13C{1H} NMR (C6D6, 295 K): δ 4.5, 5.1, 5.4, 6.0, 7.1, 7.2 (Si(CH3)2), 9.8 (HC(Si...)3), 24.1, 24.8, 27.8 (HCCH3), 55.8, 56.4, 57.8 (HCCH3), 124.2-131.2 (C2,6,C4, C3,5 of C6H5), 150.0, 150.7, 154.0 (C1 of C6H5). 7Li{1H} NMR (C6D6, 295 K): δ -0.25. 29Si{1H} NMR (C6D6, 295 K): δ -1.9, -1.0, 0.5. Anal. Calcd for C31H46LiN3Si3Sn: C, 55.42; H, 6.91; N, 6.26. Found: C, 55.30; H, 7.11; N, 6.02. Data for 2 are as follows. 1H NMR (C6D6, 295 K): δ -0.90 (s, HC(Si...)3), -0.22, 0.10, 0.14, 0.28, 0.51, 0.54 (s, Si(CH3)2), 1.15 (m, CH2CH2O), 1.52, 1.61, 2.02 (d, 3JHH ) 6.7, 6.8, 6.8 Hz, HCCH3), 3.22 (m, CH2CH2O), 4.35, 4.56, 5.05 (q, HCCH3), 6.77-7.79 (m, C6H5). Anal. Calcd for C35H54LiN3OSi3Sn: C, 56.60; H, 7.33; N, 5.66. Found: C, 56.22; H, 7.05; N, 5.78. (9) Crystal data for 2: C35H54LiN3OSi3Sn, Mr ) 742.72, orthorhombic, space group P212121, a ) 8.2893(2) Å, b ) 20.8243(4) Å, c ) 21.9993(4) Å, V ) 3797.5(2) Å3, T ) 23 °C, Z ) 4, Dc ) 1.299 g cm-3, F(000) ) 1552, µ(Mo KR) ) 0.796 mm-1. R ) 0.032 and Rw ) 0.038 with R ) ∑||Fo| - |Fc||/∑|Fo| and Rw ) [∑w(|Fo| - |Fc|)2/∑wFo2]0.5.
© 1996 American Chemical Society
3638 Organometallics, Vol. 15, No. 17, 1996
Figure 1. Molecular structure of 2. Principal bond lengths (Å) and interbond angles (deg): Sn(1)-N(1) ) 2.215(6), Sn(1)-N(2) ) 2.118(7), Sn(1)-N(3) ) 2.190(6), N(1)-Li(1) ) 2.09(2), N(3)-Li(1) ) 2.06(2), O(1)-Li(1) ) 1.95(1); N(1)Sn-N(3) ) 82.6(2), N(1)-Sn-N(2) ) 99.2(2), N(2)-SnN(3) ) 102.0(3), Sn(1)-N(3)-Li(1) ) 85.4(5), Sn(1)-N(1)Li(1) ) 83.9(5).
has previously not been observed in tripodal amido complexes containing a trisilylmethane backbone due to steric repulsion of the methyl groups. While the signal patterns in the NMR spectra of 1 and 2 indicate closely related structures and are consistent with a retention in solution of the structural arrangement established for the solid, both compounds differ significantly with respect to dynamic behavior in solution. The coordinated THF ligand appears to “lock” the Li cation in its position between the two N atoms, thus conferring structural rigidity upon the molecule on the NMR time scale. On the other hand, the nonsolvated compound 1 displays remarkable dynamic behavior. As 1H-EXSY studies have revealed, the Li atom appears to “rotate” around the N3Sn unit, generating an effective 3-fold molecular symmetry in the fastexchange limit. This intramolecular motion is reminiscent of the dynamic behavior reported by Veith and coworkers for a tetraamidoindate,10 although it appears to occur much more rapidly in the latter case. In order to assess the properties of 1 and 2 as metal nucleophiles, their reactivity toward CH3I, Me3SnCl, and Ni(CO)4 (and thus the displacement of both anionic and neutral “nucleofuges”) was studied (Scheme 2).11 All three reactions yielded products possessing molecular (10) Veith, M.; Zimmer, M.; Mu¨ller-Becker, S. Angew. Chem., Int. Ed. Engl. 1993, 32, 1731. (11) Data for 3 are as follows. 1H NMR (C6D6, 295 K): δ -0.77 (s, HC(Si...)3), -0.61 (s, SnCH3), 0.37, 0.39 (s, Si(CH3)2), 1.24 (d, 3JHH ) 6.6 Hz, HCCH3), 4.36 (q, HCCH3), 7.04-7.38 (m, C6H5). 13C{1H} NMR (C6D6, 295 K): δ -24.4 (SnCH3, 2JSnH ) 73 Hz), 5.4, 6.1 (Si(CH3)2), 7.8 (HC(Si...)3), 26.0 (HCCH3), 53.9 (HCCH3), 126.6, 127.6, 128.3 (C2,6,C4, C3,5 of C6H5), 148.9 (C1 of C6H5). 29Si{1H} NMR (C6D6, 295 K): δ 5.3. 119Sn{1H} NMR (C D , 295 K): δ -41.2 Anal. Calcd for C H N Si 6 6 32 49 3 3 Sn: C, 56.53; H, 7.27; N, 6.18. Found: C, 56.32; H, 7.36; N, 5.97. Data 1 for 4 are as follows. H NMR (C6D6, 295 K): δ -0.79 (s, HC(Si...)3), -0.27 (s, SnCH3, 2JSnH ) 54 Hz, 3JSnH ) 26 Hz), 0.31, 0.38 (s, Si(CH3)2), 1.55 (d, 3JHH ) 6.6, HCCH3), 4.52 (q, HCCH3), 7.10-7.61 (m, C6H5). 13C{1H} NMR (C D , 295 K): δ -6.2 (SnCH ), 6.5, 6.6 (Si(CH ) ), 8.8 6 6 3 3 2 (HC(Si...)3), 27.0 (HCCH3), 55.9 (HCCH3), 126.7, 127.7, 128.4 (C2,6,C4, 3,5 1 29 1 C of C6H5), 148.9 (C of C6H5). Si{ H} NMR (C6D6, 295 K): δ 4.5. 119Sn{1H} NMR (C D , 295 K): δ -50.2 (N Sn), -94.9 (SnCH ). Anal. 6 6 3 3 Calcd for C34H55N3Si3Sn2: C, 49.37; H, 6.70; N, 5.08. Found: C, 49.21; 1 H, 6.78; N, 4.89. Data for 5 are as follows. H NMR (d6-DMSO, 295 K): δ -1.09 (s, HC(Si...)3), -0.30, -0.00 (s, Si(CH3)2), 1.66 (d, 3JHH ) 6.8 Hz, HCCH3), 1.84 (m, CH2CH2O), 3.70 (m, CH2CH2O), 4.76 (q, HCCH3), 7.18-7.61 (m, C6H5). 13C{1H} NMR (d6-DMSO, 295 K): δ 6.8, 7.3 (Si(CH3)2), 11.1 (HC(Si...)3), 25.1 (CH2CH2O), 25.5 (HCCH3), 55.2 (HCCH3), 67.9 (CH2CH2O), 124.9, 127.0, 127.4 (C2,6,C4, C3,5 of C6H5), 150.0 (C1 of C6H5), 201.7 (CO). 7Li{1H} NMR (d6-DMSO, 295 K): δ 1.1. 29Si{1H} NMR (d6-DMSO, 295 K): δ 2.0. 119Sn{1H} NMR (d6DMSO, 295 K): δ 195.5. IR (toluene): ν(CO) 1987 (s, br), 1964 (sh) cm-1. Due to facile loss of THF upon isolation a correct elemental analysis could not be obtained.
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Figure 2. Structure of the HC(Me2SiNC(H)MeC6H5)3SnNi(CO)3 anion in the solid-state structure of 5. The Li(THF)4 cation is omitted for clarity. Selected bond lengths (Å) and interbond angles (deg): Sn(1)-N(1) ) 2.086(6), Sn(1)-Ni(1) -) 2.492(2), Si(1)-N(1) ) 1.720(7), N(1)-C(1) ) 1.46(1), Ni(1)-C(13) ) 1.77(1); N(1)-Sn-N(1a) ) 99.1(2), C(13)-Ni(1)-C(13a) ) 116.0(2). Scheme 2
C3 symmetry. In view of the highly crystalline nature of the Sn-Ni heterobimetallic complex 5, the latter was chosen for an X-ray crystallographic study (Figure 2).12 Although the anionic complex [(Ph3Sn)Ni(CO)3]- was first reported by Kruck et al. in 1969,13 there has been no report of a crystal structure of an [(R3Sn)Ni(CO)3]anion to date. Crystals of 5 were found to be extremely air- and moisture-sensitive, instantaneously turning opaque when isolated due to loss of lattice solvent. Therefore, the flask as well as the flushing argon were cooled to ca. -80 °C during crystal selection. Crystals were handled and transferred to the diffractometer at about -80 °C, and data were collected at -120 °C.14 The trisilylmethane and triamidostannate units are part of (12) Crystal data for 5: C54H86LiN3O8Si3NiSn, Mr ) 1173.87, cubic, space group P213, a ) 1.8298(2) Å, V ) 6126.2(12) Å3, T ) -153 °C, Z ) 4, Dc ) 1.273 g cm-3, F(000) ) 2472, µ(Mo KR) ) 0.823 mm-1. R1(F > 4σ(F)) ) 0.048 and wR2 ) 0.141 (all data) with R1 ) ∑||Fo| - |Fc||/ ∑|Fo| and wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo2)2]0.5 (Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467. Sheldrick, G. M. SHELXL-96, Program for Crystal Structure Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1996). (13) Kruck, T.; Herber, B. Angew. Chem., Int. Ed. Engl. 1969, 8, 679. (14) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615.
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a [2.2.2]bicyclooctane-related cage with one of the bridgehead positions being occupied by the Sn-Ni(CO)3 fragment. The Sn(1)-Ni(1) vector is aligned along the 3-fold crystallographic axis imposing exact C3 symmetry upon the anion. The lithium atom of the Li(THF)4+ cation is also located on the 3-fold axis, whereas the oxygen atom and the center of the opposite CH2-CH2 bond of one THF molecule are close to it. This imposes a 3-fold disorder upon this single THF molecule with site occupation factors of 0.33 each. The approximately tetrahedral coordination sphere of the lithium cation is completed by another THF molecule on a general position, resulting in three additional coordinated solvent molecules. The Sn-Ni bond length of 2.492(2) Å lies within the previously observed range found for Sn-M heterobimetallics (M ) 3d transition metal).15 The coordination of the Lewis acidic Ni(CO)3 fragment to the Lewis basic stannate effects a significant contraction of the Sn-N distances (Sn(1)-N(1) ) 2.086(6) Å) (15) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. Rev. 1989, 89, 11.
Organometallics, Vol. 15, No. 17, 1996 3639
in comparison to 2 (average Sn-N ) 2.174(6) Å). The stannate ligand is readily displaced from the nickel by better donors such as phosphines and isocyanides. In conclusion, we have provided a facile access to the first example of an enantiomerically pure chiral stannate and have established its nature as a metal nucleophile. The reactivity of this species is currently being investigated. Acknowledgment. We thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for financial support and Wacker Chemie AG for generous gifts of basic chemicals. Thanks are also due to Professor H. Werner (Wu¨rzburg, Germany) for his continued interest and support of this work. Supporting Information Available: Text giving preparative procedures for compounds 3-5 and tables of crystal data, fractional coordinates, bond lengths and angles, anisotropic displacement parameters, and hydrogen atom coordinates and figures giving additional views of 2 and 5 (21 pages). Ordering information is given on any current masthead page. OM960324P
